Rename the global inference task and reduce it's API surface by introducing the

tests/compiler/dart2js/map_tracer_const_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 
 import 'compiler_helper.dart';
 import 'type_mask_test_helper.dart';
 
@@ skipping 16 matching lines @@
   print(closure(22));
 }
 ''';
 
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri,
       expectedErrors: 0, expectedWarnings: 0);
   compiler.stopAfterTypeInference = true;
   asyncTest(() => compiler.run(uri).then((_) {
-    var typesTask = compiler.typesTask;
-    var typesInferrer = typesTask.typesInferrer;
+    var commonMasks = compiler.commonMasks;
+    var typesInferrer = compiler.globalInference.typesInferrer;
     var element = findElement(compiler, 'closure');
     var mask = typesInferrer.getReturnTypeOfElement(element);
-    Expect.equals(typesTask.numType, simplify(mask, compiler));
+    Expect.equals(commonMasks.numType, simplify(mask, compiler));
   }));
 }